Mytilus edulis and piddocks on eulittoral firm clay

LR.MLR.MytPid

LR.MLR.MytPid recorded () and expected () distribution in Britain and Ireland (see below)

Marine natural heritage importance

Listed under

EC Habitats Directive

National importance

Rare

Habitat Directive feature (Annex 1)

ReefsLarge shallow inlets and baysEstuaries

Biotope importance

Dense beds of bivalve suspension feeders increase turnover of nutrients and organic carbon in estuarine (and presumably coastal) environments by effectively transferring pelagic phytoplanktonic primary production to secondary production (pelagic-benthic coupling) (Dame, 1996). Suspension feeding Mytilus beds can deplete the seston (organic particulates) available downstream of them and are probably important in energy flow within the wider ecosystem (Holt et al., 1998). Mussel eggs and larvae from mussel beds (including subtidal beds) are probably an important food source for herring larvae and other zooplankton (Kautsky 1981; Seed & Suchanek, 1992).

The Mytilus edulis beds provide an important food source for Carcinus maenas and may provide refuge for other fauna (see habitat complexity above). Mytilus edulis are important food sources for wildfowl, and Mytilus is a staple food for oystercatchers and eider ducks. For example, unprecedentedly low stocks of Mytilus edulis in the Dutch Wadden Sea resulted in eider ducks either dying or leaving the area, while oystercatchers sought alternative food, depleting stocks of Mya arenaria and Cerastoderma edule (Holt et al, 1998). The piddocks may also represent an important food source for wildfowl and wading birds. In addition, their empty burrows provide habitat for associated fauna (see habitat complexity above).

Exploitation

Large Mytilus edulis reefs and beds have been the subject of fisheries for at least the past 100 years, and Mytilus edulis is also the subject of cultivation (Holt et al., 1998). However, small, eulittoral patches are highly unlikely to be subject to large scale exploitation. See sensitivity section for further detail.

Pholas dactylus is also known to be harvested in Britain but not to the same extent. In Italy, harvesting of piddocks has had a destructive impact on habitats and has now been banned (E. Pinn, pers. comm. to MarLIN). In Britain, collection of piddocks is thought to have a similarly destructive effect. People have been known to go out onto the shore and, with the use of a hammer and chisel, excavate the piddocks from the soft rock (K. Hiscock, pers. comm.). Farming methods are being investigated as an alternative and it is therefore possible that further targeted extraction could be a future possibility.

Additional information

The mussels and piddocks in this intertidal biotope may represent an important food source for wildfowl and wading birds.